A process as described above is conventionally carried out in plants intended for the production of commercial hydrogen peroxide solutions. For economic reasons (cf. Process Economic Report No. 68B, Hydrogen Peroxide, Marc 1992, chapter VI, SRI International) essentially linked with transportation and storage costs, these solutions must have a hydrogen peroxide concentration which is as high as possible, that is a concentration higher than 35%, more generally a concentration of 60% or 70% by weight.
With a view to preparing these concentrated, commercial hydrogen peroxide solutions the procedure is such as to recover at the exit of the extractor (stage (c)) a solution which has a hydrogen peroxide concentration that is as high as possible, while remaining outside the explosiveness region of the mixtures of working solutions and aqueous hydrogen peroxide solutions. In this context, patent application FR-A-2 228 717 shows that the hydrogen peroxide concentration of the said aqueous solution leaving the extractor must not be higher than 600 g/l, that is 50% by weight of hydrogen peroxide. A hydrogen peroxide concentration higher than this value is described as being capable of causing explosive reactions.
To obtain highly concentrated aqueous hydrogen peroxide solutions the operational parameters of the abovementioned autooxidation process are adapted so as to permit the use of a working solution which has a hydrogen peroxide equivalent that is as high as possible, for example a hydrogen peroxide equivalent higher than 11 g/l, or even more. Thus, patent application FR-A-2 086 166 recommends the use of a working solution capable of producing, after oxidation, a quantity of hydrogen peroxide of the order of 16 g/liter of working solution. However, such a conventional process using a high hydrogen peroxide equivalent has numerous disadvantages. Thus, this conventional process generally requires the use of high hydrogenation (stage (a)) and oxidation (stage (b)) temperatures. In this context, reference may be made to "Techniques de l'Ingenieur, chapitre "Peroxyde d'hydrogene" "Techniques for the Technologist, "Hydrogen peroxide," chapter!, J 6 020, which mentions that the hydrogenation and oxidation temperatures must be between 60 and 80.degree. C.
Another disadvantage encountered by the use of the conventional process is that the working solution is rapidly degraded.
In addition, this conventional process is very sensitive to the presence of water, even in small quantity, which can be introduced accidentally either into the oxidizer or into the lines connecting the oxidizer and the extractor. In this region water reacts with the oxidized working solution, and this can cause explosive reactions.